This is more a copy-paste code than a real tutorial, but hey, anyways:

<?php $visitorip = $_SERVER['REMOTE_ADDR'];echo "$visitorip"; ?>

What we do with this, is request the visitor's ip and assign it a name, visitorip, then we output it with an echo. Paste the code where you want the ip to show. Of course, before and after the code (or you can include it), you can give it format and add anything you want, just don't touch the code between < and > if you don't know how php works. Want an example? sure!